<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>

</body>
<script>
  // var str = 'str1';
  // str = str.concat('str2', 'str3');
  // console.log(str);

  var str = 'str_str';
  str = str.substr(1, 5);
  console.log(str);
</script>
</html>